1. Field of the Invention
The present invention relates to a rotary cutting tool supported by a cutting tool holder, and more particularly to a rotary cutting tool suitable for heavy cutting work of barely machinable materials, such as titanium, inconel and the like.
2. Description of the Prior Art
As one example of the above-mentioned type of cutting tool holders developed in the prior art, a rotary cutting tool holder shown in FIG. 8 has been known. In this figure, an axial bore for inserting a rotary shaft 32 is provided at a tip end portion of a cutting tool holder 1'. The rotary shaft 32 is inserted into this axial bore and is supported by a radial bearing 33 and a thrust bearing 34, and is fixed to the cutting tool holder 1' via a thrust bearing 35 and by means of a nut 36. At the axial end of the rotary shaft 32 is fixedly fitted a circular die throw-away tip 37.
Since the rotary shaft 32 is inclined by an angle .alpha..degree. with respect to a vertical axis of the cutting tool holder 1', as shown in FIG. 9, during cutting work, the circular die throw-away tip 37 can cut while it is rotating in a fixed direction due to a principal component force of a cutting resistance force (See FIG. 7).
Accordingly, the entire circumferential edge of the circular die throw-away tip 37 serves as a cutting edge and is worn out uniformly, and therefore the life of the tool can be greatly improved. In addition, impacts upon intermittent cutting work can be mitigated and chipping of the cutting edge also can be prevented (See Laid-Open Japanese Utility Model Specification 2-51005 (1990)).
However, in heavy cutting work such as roughing and the like, the heretofore known cutting tools as described above would involve the following problems:
(1) Due to the fact that the circular die throw-away tip 37 is fixed to the axial end of the rotary shaft 32, the rotary shaft 32 would bear a cutting resistance force in a cantilever fashion, and hence its rigidity in the radial direction of the tip is low. Consequently, chattering would occur during the cutting work, resulting in that machining cannot be achieved under satisfactory cutting conditions, and the cutting efficiency is lowered.
(2) In the event that the rotary shaft 32 and the bearings should be worn out, repairs would be necessary. During that time they cannot be used. In the case of heavy cutting, the consumption rate is especially severe.